Editing Warhammer 40,000/9th Edition Tactics/Death Guard (section)

===Deadly Pathogens===
Upgrades a single non-Grenade, non-Relic ''Plague weapon'' on a {{W40Kkeyword|Death Guard character}} or a {{W40Kkeyword|Bubonic Astartes}} unit champion by paying points and increases the unit's power rating by +1, giving the weapon S+1 and one other additional ability.  S+1's utility changes a lot if Arch-Contaminator is applying, and also if Nurgle's Gift is applying - both of them make it more and more important to select a low-S weapon for this.  To give you an idea, if you pick an S3 weapon and then both abilities apply, and you attack a T8 target, you go from wounding 11/36 of the time to wounding 20/36 of the time.  

*'''Acidic Malady:''' 15pts. -1 to the weapon's AP. A genuine waste of your time - Virulent Fever behaves like this but better on everything you can take it on.
*'''Befouling Runoff:''' 5pts. Ignores cover. Generally garbage, since the best weapons you can pick for this hit automatically, so ignoring Dense Cover is irrelevant, and ignoring Light Cover is worse than Acidic Malady's flat improvement to AP.  Hard pass.
*'''Corrosive Filth:''' 15pts. +1 damage against {{W40Kkeyword|Vehicles}}.
**Against a Vehicle, naturally the best thing you can take - but worthless against infantry, bikes, swarms, monsters, etc.
*'''Explosive Outbreak:''' 15pts. Deals an additional hit on an unmodified hit roll of 6, which is equivalent to +1 to hit only with proper stacking with full re-rolls to hit, and it works on WS2+ (bringing your expected hits per attack to 1 base).  Best on a plaguereaper, if you're going to take it.  Since this doesn't work at all with weapons that hit automatically, many of your ranged options are just off the table with this.
**Attached to a WS3+ model (including a natively WS2+ one with -1 to hit), this is a 25% increase in murder - on a WS2+ model, it's worth +20%.  
*'''Unstable Sickness:''' 10pts. Each kill inflicts an additional MW on the enemy unit on a 4+ with a hard cap of 3MWs, and you can't use the Befouled Incubators strat on the bearer.
**The opposite of Virulent Fever - the better the weapon is at murder, the more mortals it inflicts, assuming you're targeting a multi-model unit so there's something left to suffer the excess.  Against a 1-model unit, of course, this ability does nothing at all.
**That means you generally can't be bothered with this, because it helps you most when murdering things you need the least help murdering.
*'''Virulent Fever:''' 15pts.  Deals a MW on an unmodified Wound roll of 6.  The better the weapon is at wounding, penetrating saves, or damaging, the worse this ability is - low-damage, poor-AP weapons will notice it the most.  As a result, this is generally your best bet on a Lord of Virulence's Twin Plague Spewer.
**Stacks with a Biologis Purifier's Foul Infusion, which has diminishing returns - going from 0 mortals on a 6 to wound to 1 is less of a step than from 1 to 2.
*'''Viscous Death:''' 5pts. Re-roll the number of attacks for this weapon. Ideal for a Foul Blightspawn's Plague Sprayer, but since rolling more dice makes this ability worse - you have to re-roll the whole roll, you can't only re-roll poor dice - not nearly as good for a Lord of Virulence.  Genuinely makes a Blightspawn killier.

Numbers speak for themselves: the only options that are actually real upgrades in killiness per point are virulent fever, viscous death, corrosive filth (which is highly situational), and explosive outbreak (once you're in melee). Weigh them against the cost of an extra Poxwalker. All in all, these are fun options that will not weaken your army if you don’t go overboard with them.